Gradeability-based shift pattern control for an automatic transmission

• US 5,172,609 A
• Filed: 03/02/1992
• Issued: 12/22/1992
• Est. Priority Date: 03/02/1992
• Status: Expired due to Fees

• Current Assignee: Saturn (CCL Industries Incorporated)
• Original Assignee: Saturn (CCL Industries Incorporated)
• Inventors: Nitz, Larry T., Rees, Susan L.
• Primary Examiner(s): Braun, Leslie A.
• Assistant Examiner(s): TROUSDELL, WILLIAM
• Application Number:
  US07/844,063
• Time in Patent Office: 295 Days
• Field of Search: 74/856, 74/861, 74/865, 74/866, 364/424.1
• US Class Current: 477/97
• CPC Class Codes: F16H 2061/0209 with independent solenoid valves modulating the pressure individually for each clutch or brake
• CPC Class Codes: F16H 2061/161 by checking feasibility of shifts, i.e. determine if requested shift can be successfully completed and post shift values are in an acceptable range
• CPC Class Codes: F16H 59/52 dependent on the weight of the machine, e.g. change in weight resulting from passengers boarding a bus
• CPC Class Codes: F16H 59/62 Atmospheric pressure
• CPC Class Codes: F16H 59/66 Road conditions, e.g. slope, slippery
• CPC Class Codes: F16H 61/0213 characterised by the method for generating shift signals
• CPC Class Codes: F16H 61/16 Inhibiting or initiating shift during unfavourable conditions, e.g. preventing forward reverse shift at high vehicle speed, preventing engine over speed unintentional control input F16H61/18
• CPC Class Codes: F16H 61/21 Providing engine brake control
• CPC Class Codes: F16H 61/682 with interruption of drive
• CPC Class Codes: Y10S 477/90 Control signal is vehicle weight

Abstract

An improved shift pattern control in which successive upshifting and downshifting is avoided in conditions of above normal loading by inhibiting upshifting to a speed ratio having insufficient gradeability in relation to a measure of the actual loading. In essence, the control continually monitors the gradeability of the various forward speed ratios of the transmission in relation to a measure of the actual grade load to determine their excess gradeability, and removes from the shift pattern those speed ratios having insufficient excess gradeability. This ensures that the transmission will never be upshifted to a speed ratio that has insufficient gradeability for the given driving condition, thereby eliminating the successive upshifting and downshifting which occurs with conventional shift controls.

Claims

1. In a motor vehicle including an engine and a transmission providing a plurality of forward speed ratios through which the engine may drive the vehicle, a method of operation comprising the steps of:

initiating upshifting and downshifting between said speed ratios in response to a comparison of measured load condition parameters with predetermined load condition parameters defined by a base shift pattern;

determining an apparent grade load indication in relation to an imbalance between engine produced torque and an estimate of the torque required to achieve a current driving condition of the vehicle;

determining maximum gradeability indications corresponding to a maximum grade load which can be overcome with said forward speed ratios;

comparing said apparent grade load with said maximum gradeability indications to form an indication of excess gradeability of each such speed ratio; and

overriding said base shift pattern when an excess gradeability indication for a respective speed ratio is less than a reference value by inhibiting upshifting to such respective speed ratio.

2. The method of operation set forth in claim 1, including the step of:

increasing a maximum gradeability indication for a given speed ratio in relation to an estimate of a transmission input speed which would occur in a successively lower speed ratio, so as to prevent overriding of said base shift pattern which would produce undesirably high input speed during engine braking conditions.

3. The method of operation set forth in claim 1, wherein the step of determining maximum gradeability indications includes the steps of:

retrieving predetermined gradeability values corresponding to the maximum gradeability of said forward speed ratios at sea level; and

adjusting said gradeability values in relation to an indication of ambient barometric pressure to form said maximum gradeability indications.

4. In a motor vehicle including an engine, a transmission providing a plurality of successively increasing forward speed ratios through which the engine may drive the vehicle, a base shift pattern control for initiating upshifting and downshifting between said speed ratios in response to a comparison of measured load condition parameters with predetermined load condition parameters, and a range selector positionable by a vehicle driver to exclude at least one specified speed ratio from said base shift pattern, a method of operation comprising the steps of:

determining an apparent grade load indication in relation to an imbalance between engine produced torque and an estimate of the torque required to achieve a current driving condition of the vehicle;

determining maximum gradeability indications corresponding to a maximum grade load which can be overcome with said forward speed ratios;

comparing said apparent grade load with said maximum gradeability indications to form an indication of excess gradeability of each such speed ratio; and

overriding said base shift pattern when an excess gradeability indication for a respective speed ratio is less than a reference value by inhibiting upshifting to such respective speed ratio.

5. Control apparatus for a motor vehicle including an engine and a transmission providing a plurality of forward speed ratios through which the engine may drive the vehicle, the control apparatus comprising:

means for initiating upshifting and downshifting between said speed ratios in response to a comparison of measured load condition parameters with predetermined load condition parameters defined by a base shift pattern;

means for determining an apparent grade load indication in relation to an imbalance between engine produced torque and an estimate of the torque required to achieve a current driving condition of the vehicle;

means for determining maximum gradeability indications corresponding to a maximum grade load which can be overcome with said forward speed ratios;

means for comparing said apparent grade load with said maximum gradeability indications to form an indication of excess gradeability of each such speed ratio; and

means for overriding said base shift pattern when an excess gradeability indication for a respective speed ratio is less than a reference value by inhibiting upshifting to such respective speed ratio.